Speech translation systems are often faced with unrecognized words or phrases in an input speech signal representing speech. These unrecognized words or phrases are often proper names of people, cities, companies, etc. Existing systems typically take one of the following actions in response to this problem:
(i) ignoring (or deleting) the unknown items, resulting in an incomplete translation of the original speech having, for example, a missing place name. PA1 (ii) finding the nearest match of the unknown segment of speech to items in the known vocabulary of the system. Since the chosen item may be unrelated in meaning to the unknown segment, this leads to incorrect or misleading translations. PA1 (iii) asking the user to rephrase the entire original phrase, resulting in confusion for the user who may not be sure why the system is not able to cope with the input.